Airsoft is a competitive team shooting sport in which participants eliminate opposing players by tagging them out of play with spherical plastic projectiles launched via replica air weapons called airsoft guns.
Although very similar to paintball in concept and game play, airsoft pellets do not typically leave visible markings on their target, and hits are not always apparent. Though the pellets can sometimes leave red contusions or “welts” on exposed skin, the game relies heavily on an honor system in which the player who has been hit is ethically obliged to call themselves out.
The airsoft guns used are mostly magazine-fed, with some having manual/battery-powered spring-piston pump power plants similar to Nerf Blasters, or pneumatically powered by replaceable compressed gas (e.g. propane (“green gas”), 1,1,1,2-tetrafluoroethane or CO2) canisters.
Many airsoft guns also have mounting platforms compatible with genuine firearm accessories, and cosmetically more resembling real firearms. This makes them popular for military simulation and historical reenactments. There are also professional gun safety and weapon manipulation trainings conducted with airsoft in some fields, such as law enforcement trainings,due to better safety and lower cost. The United States Coast Guard, for instance, has officially adopted airsoft for training in 2018.
More details and the updated laws can be found here.